It is known to use superabsorbent materials, (often superabsorbent polymers, SAP) in disposable absorbent products such as diapers, incontinence guards, sanitary napkins, panty liners and the like for absorbing e.g. urine, menses or liquid from faeces etc. Superabsorbent materials can absorb liquid in amounts which are usually several times the mass of the polymers themselves. Superabsorbent polymers are sometimes called hydrogels or gels.
Upon absorbing liquid, superabsorbent materials tend to swell. However, this can lead to a phenomenon known as “gel blocking” in which the part of the superabsorbent material which first makes contact with liquid expands and prevents liquid from penetrating further into the remainder of the superabsorbent material. Gel blocking is particularly a problem for absorbent articles which contain relatively large concentrations of superabsorbent material and which are designed to absorb relatively large amounts of liquid.
There have been a number of attempts to eliminate or overcome the problem of gel blocking. Strategies include adapting the chemical composition, distribution or concentration of the superabsorbent material itself, mixing other absorbent materials with the superabsorbent material or including additional layers of material in the absorbent article which function as reservoirs. Examples can be found in EP 0 343 941, EP 1 594 557, JP 2005 113135 and WO 2004/093931.
U.S. Pat. No. 6,342,298 describes multicomponent superabsorbent fibers which comprise at least one acidic water-absorbing resin and at least one basic water-absorbing resin. The acidic and basic resins are in close proximity so as to maximize ion exchange between the two.
US 2005/0130540 discloses a nonwoven web of multicomponent filaments. The filaments comprise superabsorbent polymer in their centre surrounded by a thermoplastic polymer sheath.
U.S. Pat. No. 6,610,898 describes the use of heat-shrunk, spiralized thermoplastic multicomponent fibres to provide an open and lofty structure in a fluid acquisition/transfer layer of an absorbent article.
WO 2004/017883 discloses an absorbent core which contains fibres coated with SAP. Some or all fibres may be only partially covered with SAP.
There remains a need, however, for simple ways in which gel blocking can be reduced. In particular, there is a need for novel superabsorbent materials which can be readily produced from known technologies, which can be manufactured from existing materials and which reduce or eliminate the problems associated with gel blocking. In addition, it is often desirable to create open structures based on superabsorbent polymers. Dynamic systems which change their physical structure, or are activated upon absorbing liquid, are also desirable.